It is known to provide diverse mechanisms to permit an object or member to be moved along a straight line path of travel relative to another member between a pair of chosen or pre-established positions. However, as far as I am aware, these prior mechanisms, with the exception of multiple piston and multiple part slide mechanisms, are not capable of permitting relative movement of the members through a distance exceeding the contracted length of the mechanism,n or are such prior mechanisms capable of permitting independent or fine adjustments of the position of the object relative to each of such pre-established positions between which the object can be alternatively and repeatedly moved in a stepwise manner.